Jump racing has been suspended at Southwell until further notice, following two further equine fatalities at the Nottinghamshire track on Thursday evening.
The British Horseracing Authority was already working with owners Arena Racing Company in looking into the circumstances of six fatalities at the venue between July 1 and August 24.
After the deaths of Cillian's Well and Day Of Roses, the BHA and ARC issued a joint statement which read: "The British Horseracing Authority and Arena Racing Company have jointly made the decision to suspend jump racing at Southwell until further notice.
"This is to allow a comprehensive investigation to take place following two further fatalities at this evening's fixture.
"A process is already under way to investigate the circumstances around the six fatalities that occurred at the track since between July 1 and August 24.
"This involves the racecourse and the BHA's veterinary team, racecourse department and course inspectors looking into the specific circumstances to understand if there are any common factors."
The statement added: "Following this evening's fixture, jump racing will not take place at Southwell until further notice whilst a comprehensive review is carried out.
"These fixtures will be rescheduled at alternative jump racecourses with details to be announced in the coming days."
ARC said in a statement: "In light of an unacceptable number of fatal injuries incurred at recent meetings, ARC will continue and expedite a comprehensive review and investigation, working closely with BHA and horsemen.
"There will be a full review into all possible factors, including (but not limited to) fence and hurdle design, track layout and configuration and going as well as GPS speed and timing data. It will also consider horse ratings.
"Jump racing will only return to Southwell when ARC and the BHA are satisfied that all necessary measures to mitigate against injuries at the track have been implemented, so enabling jump racing to return with confidence."
Brant Dunshea, chief regulatory officer at the BHA, said: "The BHA and ARC met earlier this week and agreed a series of immediate measures which were put in place for this evening's meeting.
"The course was inspected prior to racing by a BHA course inspector and was deemed fit to race. Pre-race checks were also carried out on all horses competing by BHA veterinary officers.
"In the sad event of two further fatalities, we have jointly decided with ARC to suspend jump racing at Southwell until further notice whilst we work together to complete a detailed investigation."
There were 173 equine deaths from 91,937 runners in 2019, according to BHA figures - representing a fatality rate of 0.19 per cent of runners - while faller rates last year reached an all-time low of 2.37 per cent.